Life Hacker calls this this an anti-theft lunch bag. It is sold here.
If office gremlins are making off with your daily meal, innovative designer Sherwood Forlee has a clever solution: the Anti-Theft Lunch Bag. Simply put, Anti-Theft Lunch Bags "are regular sandwich bags that have green splotches printed on both sides." With your sandwich inside, the bag simulates mold and makes the contents look disgusting. These bags aren't available for purchase, but the idea shouldn't be difficult to replicate if you need more sandwich security at your workplace.
Yes, it would discourage someone in your office from eating your sandwhich. The real problem with this faux moldy sandwhich bag is that it might encourage someone to throw it away.
